A redox (reduction-oxidation) flow battery is a rechargeable battery or fuel cell that includes liquid electrolytes within tank(s). The liquid electrolytes are separated from one another, e.g., by a selective membrane, to promote ion exchange and thus electric current flow. A redox flow battery's separable liquids provide increased longevity as compared to other battery types.
The redox flow battery may be recharged by pumping additional electrolyte solution through the cell(s). The redox flow battery also permits capture and recycling of spent electrolyte solution. The redox flow battery is therefore akin to other electrochemical cells, but provides externally stored electrolyte solution to a reactor in order to generate electricity, rather than having ionic solution stored in the cell around the electrodes.
Redox flow battery energy capacity, e.g., measured as the amount of current that is produced, is a function of the amount of electrolyte that is available. Thus, redox flow batteries, e.g., connected to a commercial power grid or other power supply as a backup energy generation system or power source, are often quite large in size. For example, a redox flow electrolyte tank may contain many liters or gallons of electrolyte fluid.